CN114207250B - System and method for repairing high temperature gas turbine components - Google Patents

Abstract

A method of forming a component comprising: mixing a powdered base material and a binder to define a mixture, forming the mixture into a desired shape without melting the base material, removing the binder from the desired shape to define a skeleton, the skeleton having a volume between 80 and 95 percent of the base material, and infiltrating the skeleton with a melting point depressant material to define a finished part having a porosity of less than one percent by volume.

Description

System and method for repairing high temperature gas turbine components

Technical Field

The present disclosure relates generally to systems and methods for repairing high temperature gas turbine components, and more particularly to such systems and methods for repairing gas turbine blades and vanes.

Background

The difficulties associated with Additive Manufacturing (AM) of nickel-based gas turbine components having high gamma prime content make the process unsuitable for large-scale manufacturing or repair. In particular, attempts to additively manufacture components using alloy (CM) 247 or repair such components often result in grain boundary melting and cracking. Alternatively, the component is repaired with another worse nickel-based alloy that is less prone to cracking, resulting in poor component performance.

Disclosure of Invention

A method of forming a component comprising: mixing a powdered base material and a binder to define a mixture, forming the mixture into a desired shape without melting the base material, removing the binder from the desired shape to define a skeleton, the skeleton having a volume between 80 and 95 percent of the base material, and infiltrating the skeleton with a melting point depressant material to define a finished part having a porosity of less than 1 percent by volume.

In another configuration, the component includes a skeleton formed from a base material and defining a final shape of the component, the skeleton having a porosity of between 5 and 20 percent, and a melting point depressant material disposed within the skeleton, the melting point depressant material filling voids within the skeleton to define a finished component having a porosity of less than 1 percent by volume.

The foregoing has outlined rather broadly the features of the present disclosure so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages of the disclosure will be described hereinafter that form the subject of the claims. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure in its broadest form.

Additionally, before the following detailed description is made, it is to be understood that various limitations on certain words and phrases are provided throughout this specification, and one of ordinary skill in the art will understand that in many, if not most instances, such limitations apply to prior, as well as future uses of such limited words and phrases. While certain terms may include a variety of embodiments, the appended claims may expressly limit these terms to particular embodiments.

Drawings

FIG. 1 is a longitudinal cross-sectional view of a gas turbine engine.

FIG. 2 is a perspective view of a number of buckets of the gas turbine engine of FIG. 1.

FIG. 3 is a perspective view of an insert for use in repairing the turbine bucket of FIG. 2.

FIG. 4 is a perspective view of the bucket of FIG. 2 with the insert of FIG. 3 being installed.

Fig. 5 is a perspective view of a component 3D printed in near net shape.

Fig. 6 is a perspective view of the component skeleton after binder removal and sintering.

Fig. 7 is a perspective view of the component skeleton during penetration of the melting point depressant.

Fig. 8 is a perspective view of the finished near net shape component after infiltration.

Fig. 9 is a perspective view of another component 3D printed in a near net shape.

Fig. 10 is a perspective view of the component skeleton of fig. 9 after binder removal and sintering.

Fig. 11 is a perspective view of the component skeleton of fig. 9 during permeation of the melting point depressant.

Fig. 12 is a perspective view of the finished near net shape component after infiltration and during removal of the gate.

Fig. 13 is a perspective view of an attachment PSP for use in a leading edge repair process.

Fig. 14 is a perspective view of a leading edge replacement part attached to the attachment PSP of fig. 13.

FIG. 15 is a perspective view of a portion of a gas turbine blade having operational damage in the form of tip erosion and tip cracking.

Fig. 16 is a perspective view of the blade of fig. 15 with the damaged portion of the blade removed.

FIG. 17 is a perspective view of an alternate tip for repairing the damaged blade of FIG. 16.

Fig. 18 is a perspective view of an attachment PSP for use in repairing the blade tip of fig. 16.

Fig. 19 is a perspective view of the damaged blade of fig. 16, the attachment PSP of fig. 18, and the replacement tip of fig. 17.

Fig. 20 is a perspective view of an alternate tip in "green form" during the manufacturing process.

Fig. 21 is a perspective view of the replacement tip of fig. 20 after sintering and removal from manufacturing the support member.

Fig. 22 is a perspective view of the alternate tip of fig. 21 mounted to the blade of fig. 16.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

Detailed Description

Various techniques related to systems and methods will now be described with reference to the drawings, in which like reference numerals refer to like elements throughout. The drawings discussed below and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged device. It is to be understood that functions described as being performed by certain system elements may be performed by multiple elements. Similarly, for example, elements may be configured to perform functions described as being performed by multiple elements. Many novel teachings of the present application will be described with reference to exemplary, non-limiting embodiments.

In addition, it is to be understood that the words or phrases used herein should be construed broadly unless otherwise limited by the context clearly. For example, the terms "comprising," "having," and "containing," as well as derivatives thereof, mean inclusion without limitation. The singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term "or" is inclusive, meaning and/or, unless the context clearly dictates otherwise. The phrases "associated with … …" and "associated therewith" and derivatives thereof may mean included, included within … …, interconnected with … …, contained within … …, connected to or connected with … …, coupled to or connected with … …, communicable with … …, mated with … …, interleaved, juxtaposed, proximate, coupled to or combined with … …, having the properties of … …, and the like. Furthermore, while various embodiments or configurations may be described herein, any features, methods, steps, components, etc. described with respect to one embodiment are equally applicable to other embodiments without specific recitation of the contrary.

Furthermore, although the terms "first," "second," "third," and the like may be used herein to connote various elements, information, functions, or acts, the elements, information, functions, or acts should not be limited by the terms. Rather, these numerical adjectives are used to distinguish one element, information, function or act from another. For example, a first element, first information, first function, or first action may be termed a second element, second information, second function, or second action, and, similarly, a second element, second information, second function, or second action may be termed a first element, first information, first function, or first action without departing from the scope of the present disclosure.

Furthermore, unless the context clearly indicates otherwise, the term "adjacent" may mean: an element is relatively close to but not in contact with another element; or the element may be in contact with other parts. Furthermore, unless explicitly stated otherwise, the phrase "based on" is intended to mean "based, at least in part, on". The term "about" or "substantially" or similar terms are intended to encompass variations in values that are within the normal industry manufacturing tolerances of that dimension. If no industry standard is available, a 20 percent variation will fall within the meaning of these terms unless otherwise indicated.

FIG. 1 illustrates a gas turbine engine or combustion turbine engine 10 including a compressor section 15, a combustion section 20, and a turbine section 25. During operation, atmospheric air is drawn into the compressor section 15 and compressed. A portion of the compressed air is mixed with fuel and combusted in the combustion section 20 to produce high temperature combustion products. The combustion products mix with the remaining compressed air to form exhaust gas, which then passes through the turbine section 25. The exhaust gases expand within turbine section 25 to generate torque that powers compressor section 20 and any auxiliary devices attached to engine 10, such as an electrical generator. The exhaust gas enters the turbine section 25 at high temperatures (1000°f, 538 ℃ or higher) such that the turbine blades 30 and vanes are exposed to high temperatures and must be fabricated from materials that accommodate those temperatures. The terms blade and vane should be read interchangeably. Although the term "blade" refers generally to a rotating airfoil and "bucket" refers to a stationary airfoil, the invention should not be limited to these limitations, as most repairs or treatments are equally applicable to both blades and buckets.

In one configuration, the vane 30 is fabricated from a nickel-based superalloy such as alloy (CM) 247. FIG. 2 illustrates a portion of a stationary vane 30 from the turbine section 25 of the engine 10 of FIG. 1. Each bucket 30 includes a leading edge 35, a trailing edge 40, a suction side 45, and a pressure side 50. Adjacent vanes 30 cooperate with one another to define a flow path between adjacent vanes 30. The exhaust gas is directed and accelerated through the flow path and as desired to provide efficient expansion of the exhaust gas and torque to the rotor 53, which rotor 53 in turn drives the auxiliary equipment.

During operation, the bucket 30 may be damaged. Damage may be caused by foreign body impact, high temperature operation, fatigue, creep, oxidation, and the like. One area susceptible to damage is the leading edge 35 of the vane 30. FIG. 2 illustrates one of the vanes 30 with a portion 55 of the leading edge 35 removed. The desired repair will include replacing the removed portion 55 with a material that closely matches the base material. However, nickel-based superalloys such as the nickel-based superalloys used to fabricate the bucket 30 are detrimental to welding or typical additive manufacturing repair processes.

Fig. 3 and 4 illustrate one possible repair for the leading edge 35 of the bucket 30 illustrated in fig. 2. Fig. 3 illustrates an insert in the form of a leading edge insert 60, and fig. 4 illustrates the positioning of the leading edge insert 60 in the bucket 30 for attachment. The insert 60 includes a major portion that mates with the base material and is typically attached using a brazing process.

Fig. 5-12 illustrate a process for manufacturing the insert 60 illustrated in fig. 3 or any other desired repair component. Fig. 5-8 illustrate a process for a generic cube-shaped object 65, while fig. 9-12 illustrate a similar process for the leading edge insert 60 illustrated in fig. 3.

The process begins with mixing a high gamma' nickel powder 66 (base material) with a binder 67 and 3D printing or otherwise additively manufacturing the desired part 70, 75 in green form to form a near net shape. The green form parts 70, 75 are then allowed to dry. Fig. 5 and 9 illustrate this step. The base material does not melt during the printing or additive manufacturing process. As used herein, the term "near net shape" refers to a component that falls within desired manufacturing parameters and tolerances for the component at particular steps in the manufacturing process without further machining. However, some surface grinding or polishing may be required to obtain the surface finish or texture required for the finished part. Additionally, additional layers or coatings may be applied to the component to complete the component for use. Further, and as illustrated in fig. 9-12, the green form component 75 may include features such as gates 80 or support structures that are used during the manufacturing process and subsequently removed. A green form component 75 comprising features such as these would be considered a near net shape because no additional machining or handling is required before additional manufacturing steps are performed and only unwanted features (gates 80) are required to be removed.

The next step is to place the green form parts 70, 75 into a furnace or other heating device. The green form parts 70, 75 are heated to burn off or remove the binder 67. The remaining material defines the backbones 85, 90 of the base material 66 and the gap or void region 68 previously occupied by the adhesive material 67. In fig. 6, the skeleton 85 is in a cubic shape. In fig. 10, the skeleton 90 defines an intermediate component that will ultimately become the leading edge insert 60 and further includes the gate 80. In a preferred arrangement, the heating or sintering step does not melt the base material 66 and leaves at least eighty percent of the volume of the armature 85, 90 as the base material 66, thereby leaving no more than twenty percent of the armature 85, 90 as the void space 68. This is referred to herein as twenty percent or less porosity. The amount of binder 67 used and the sintering temperature are selected to achieve a porosity of less than twenty percent, and preferably between five percent and twenty percent.

As illustrated in fig. 7 and 11, the backbones 85, 90 and the gate 80 are infiltrated with a low melting point material or melting point depressant 100 (sometimes referred to as a braze material). Preferred components of the melting point depressant 100 include at least one of titanium (Ti), zirconium (Zr), and hafnium (Hf), with the remainder being chromium (Cr) and nickel (Ni). The use of boron (B), silicon (Si), or phosphorous (P) as the melting point depressant 100 is avoided, in part or in whole, to prevent these materials from having a negative impact on the material properties of the finished components 60, 65.

To produce the desired penetration, the melting point depressant 100 is melted in a manner that ensures that the liquid melting point depressant 100 contacts the framework 85, 90. Capillary action resulting from the porosity in the skeletons 85, 90 pulls the liquid melting point depressant 100 into the pores 68 of the skeletons 85, 90 and can produce ninety nine percent filled material (i.e., one percent porosity) finished parts 60, 65.

The particular components of the melting point depressant 100 are selected based at least in part on the amount of titanium included in the base material. For example, in constructions that include 3.5 percent or more titanium by weight in the base material, the desired melting point depressant 100 includes at least one of Hf and Zr, with the remainder being Ni and Cr. In constructions having 1.0 percent or less titanium in the base material, preferred components include titanium with the remainder being Ni and Cr. When the amount of Ti in the base material is between 1.0 percent and 3.5 percent, the desired component includes at least one of Zr and Ti, with the remainder being Ni and Cr. The amount of Ti, zr or Hf is selected such that the finished nickel-based component has less than 6.0 percent Ti (with other configurations having less than 5.0 percent Ti and still other configurations having less than 4.0 percent Ti).

Once infiltration is complete, any features added for manufacturing requirements, such as the gate 80 or support structure illustrated in fig. 9-12, are removed to complete the components 60, 65. Any additional grinding, polishing or layer addition may now be performed prior to mounting the components 60, 65 as shown in fig. 4. In a preferred configuration, the components 60, 65 have less than one percent porosity after infiltration.

The process described herein does not melt the base material powder 66. Instead, the powder 66 is mixed with the binder 67, 3D printed using a laser or other energy source, and dried. The adhesive 67 is burned off at low temperatures (e.g., < 500 ℃). The remaining base material 66 is heated to a sintering temperature that ensures that a maximum of twenty percent porosity remains in the sintered material.

For nickel-based alloys, the amount of titanium employed is preferably limited to about six percent (i.e., between four and eight percent) to reduce the likelihood of reduced mechanical properties. Because of this limitation, the level of porosity in the backbones 85, 90 is determined, at least in part, by the amount of titanium in the base material and in the braze material 100 (sometimes referred to as a melting point depressant), with the goal being about six percent titanium in the finished component 60, 65. For example, in one configuration, the base material or armature 85, 90 may not include titanium. If a braze material containing 22% titanium is used, the total porosity of the backbones 85, 90 will be limited to about 30%, which results in a finished part 60, 65 having about 6.6% titanium.

In another example, the backbones 85, 90 comprise 1% titanium. In this case, using the same brazing material with 22% titanium, the skeletons 85, 90 should be limited to less than 20% porosity to give finished parts 60, 65 with about 5.2% titanium.

In yet another example, the backbones 85, 90 comprise 2% titanium. In this case, using the same brazing material with 22% titanium, the skeletons 85, 90 should be limited to less than 15% porosity to give finished parts 60, 65 with about 6.0% titanium.

As discussed, nickel-based gas turbine components, particularly alloy (CM) 247 components, are difficult to repair or build with any method involving component melting, due to the fact that the grain boundary melting (incipient melting) temperature is low relative to the welding temperature, such that weld repairs often develop cracks during the repair process.

As discussed with respect to fig. 2-12, an alternative to weld repair is to first construct a replacement part 60, 65 (pre-sintered preform (PSP)) for the damaged section of the bucket 30 and then join the new replacement part 60, 65 to the part being repaired (e.g., the bucket 30) using a process that ensures that the highest temperature remains below the grain boundary melting temperature. To further improve such repair, one can replace the damaged section of the part being repaired with a replacement part 60, 65, the replacement part 60, 65 comprising the following functional materials: the functional material provides a higher oxidation resistance than the base material of the component being repaired (e.g., bucket 30).

The damaged portion 55 is removed and replaced with a close-fitting replacement part 105, the replacement part 105 being made using an Additive Manufacturing (AM) material or a pre-sintered preform (PSP) that provides similar or better oxidation and fracture characteristics. When replacement component 105 is a replacement for leading edge 35 as illustrated in fig. 2-4 and 9-12, replacement component 105 for additive manufacturing may include columnar grains with significant fracture capability.

To perform repair of the leading edge 35 with a highly oxidation resistant material, the damaged portion 55 of the leading edge 35 of the bucket 30 is first removed. The removed damaged portion 55 is measured to determine the size and configuration of the replacement component 105 to be installed. The replacement part 105 is then manufactured using an additive manufacturing process or the replacement part 105 is manufactured as a PSP, such as the PSP manufactured using a process as described with respect to fig. 2-12. In order to enhance the oxidation resistance of the replacement part 105, the material used to fabricate the replacement part 105 when using the additive manufacturing process includes at most eight percent (8%) aluminum. In addition, attachment structures 110, such as pins, protrusions, notches, apertures, etc., may be formed as part of the replacement component 105 to enhance or create an interlock between the replacement component 105 and the bucket 30 or other component being repaired.

When replacement component 105 is manufactured as a PSP, preferred materials include up to eighty percent (80%) superalloy (preferably matching bucket 30 being repaired), up to eight percent (8%) aluminum, and up to thirty percent (30%) braze material including Ti, zr, and Hf as described above. As with the additively manufactured replacement component 105, the PSP replacement component 105 may include attachment structures 110 similar to those described above. Fig. 9 and 10 illustrate an attachment structure 110 in the form of an alignment pin 111. The pins 111 align with and engage apertures formed in the blade 30 to which the replacement component 105 is to be attached. Although the pin 111 is illustrated in fig. 9 and 10 only for clarity, in a preferred configuration, the pin 111 will be formed as part of the replacement part 105 and will therefore be present in each step of the manufacturing process. In other constructions, the pins 111 are separate components that are attached to the replacement component 105 at some point during the manufacture of the replacement component 105. Attachment may be facilitated using any suitable attachment means including, but not limited to, adhesives, welding, brazing, and the like.

The material used to make the PSP replacement part 105 is maintained at a temperature at least 50 ℃ above the braze melting temperature for more than an hour to react the majority of the braze material with the base material powder. This prevents remelting during the brazing operation that attaches the replacement component 105 to the bucket 30.

The attachment PSP 115 shown in fig. 13 is formed from a material combination similar to that described above with respect to the PSP replacement part 105, except that the attachment PSP 115 includes at least thirty percent (30%) of brazing material instead of at most thirty percent (30%) of brazing material. The attachment PSP 115 is preferably no more than 250 microns thick and is produced at a similar temperature as the PSP replacement part 105 described above, but the attachment PSP 115 is held at that temperature for a shorter time (less than 15 minutes). Thus, the attachment PSP 115 has sufficient unreacted braze material to be able to join the replacement component 105 as illustrated in FIG. 14, regardless of how the replacement component 105 is manufactured (PSP or additive manufacturing), to the bucket 30 being repaired.

Due to the tailored composition and the Ni-Cr- (Ti, zr, hf) braze composition, the replacement part 105 has sufficient mechanical properties and oxidation resistance. In addition, columnar grains provide significant fracture capability of the base material beyond the equiaxed grain structure when using the additively manufactured replacement part 105.

As will be described below, these processes and procedures may be applied to other components, such as the bucket 30 or the tip 120 of the blade.

For example, fig. 15-19 illustrate a process similar to that just described, but for repair of nickel-based gas turbine blades 30 or vanes, particularly tips 120 of blades 30 or vanes made of alloy 247 or similar materials.

Fig. 15 schematically illustrates a blade 30 having a tip section crack 125 extending downward in the blade 30. Blade tip 120 also includes an oxidation damaged portion 130 that is common after operation of turbine blade 30. To repair blade 30, the damaged portion of tip 120 is first removed. In the example of fig. 15, the removal of the damaged portion 135 does not completely remove the crack 125, but the oxidized damaged portion 130 is removed. It is desirable to minimize the amount of tip 120 that is removed so that in some cases the portion with crack 125 may remain after removal. Referring to fig. 16, any cracks 125 that remain after the removal of the damaged portion 135 are removed using a machining process, grinding, or other suitable material removal process.

A closely fitting replacement tip 140 is formed to fill the space created by the removal of the damaged portion 135. The replacement tip 140 may also fill any space formed during the removal of any crack 125. Alternatively, the space that is open during the removal of the crack 125 may be filled with powdered brazing material during the attachment process for the replacement tip 140. The replacement tip 140 may be formed using an Additive Manufacturing (AM) process, or may be formed from a pre-sintered preform (PSP) that provides similar or better oxidation and fracture characteristics than the removed portion 135.

The replacement tip 140, when manufactured using the AM process, is preferably composed of a material similar to the base material of the blade 30, with the addition of up to eight percent (8%) aluminum to provide excellent oxidation resistance. In addition, an attachment structure 110, such as pin 145 illustrated in fig. 17, may be used to enhance the mechanical connection between the replacement tip 140 and the remainder of the blade 30 being repaired. Of course, other features such as protrusions, apertures, bosses, etc. may be used as the attachment structure 110. The pins 145 of fig. 17 are received in corresponding apertures formed in or otherwise present in the remainder of the blade 30 being repaired.

In a configuration using PSP instead of AM replacement tip 140, the material is preferably made of up to eighty percent (80%) superalloy (matching the base material of blade 30 being repaired), up to eight percent (8%) aluminum, and up to thirty percent (30%) braze material including Ti, zr, and Hf as described above.

The material used to make the PSP replacement tip 140 is maintained at a temperature at least 50 ℃ above the melting temperature of the brazing material for more than an hour to react the majority of the brazing material with the base material powder. This prevents remelting during the brazing operation that attaches the replacement tip 140 to the blade 30 being repaired.

The tip attachment PSP 150 shown in fig. 18 is formed from a material combination similar to that described above with respect to PSP replacement tip 140, except that tip attachment PSP 150 includes at least thirty percent (30%) brazing material instead of at most thirty percent (30%) brazing material. The tip attachment PSP 150 is preferably no more than 250 microns thick and is produced at a similar temperature as the PSP replacement tip 140 described above, but the tip attachment PSP 150 is held at that temperature for a shorter time (less than 15 minutes). Thus, regardless of how the replacement tip 140 is manufactured (PSP or additive manufacturing), the tip attachment PSP 150 has sufficient unreacted braze material to be able to join the replacement tip 140 to the blade 30 being repaired as illustrated in fig. 19.

The replacement tip 140 has sufficient mechanical properties and oxidation resistance due to the tailored composition and the Ni-Cr- (Ti, zr, hf) braze composition.

As previously described, the gas turbine components are operated under various local conditions that may create local damage. This may be due to different component conditions (e.g., temperature, pressure, fluid characteristics, etc.) and engine conditions.

One example of a local operating condition exists at the first row of turbine blades 155, where a local fault on the blades 155 may result in damage in a plurality of areas including the leading edge 160 of the blades 155 and the tips 165 of the blades 155. FIG. 22 illustrates the leading edge 160 and tip 165 of the blade 155, and also illustrates a replacement tip 170 installed for repair of cracking and/or oxidative damage at the blade tip 165.

One type of damage occurs at the leading edge 160 of the first stage blade 155 and other blades to which a ceramic coating is adhered near a series of cooling apertures 175. If the coating peels off, it is often observed that the leading edge is burned off or lost. Other areas where damage may occur are at the tip 165 of the blade 155 where the blade 155 may rub against an annular section or other component radially outward of the blade 155. Severe oxidation may also occur at the tip 165 of the blade 155 and cracks or tip cracks may form and propagate from the cooling apertures 175 or from damage caused by other factors such as friction or oxidation.

As previously described, repair of a blade or vane tip 165 may include removing a portion of the blade tip 165 and then replacing it with a replacement tip 170. Similar repairs may also be made to the blade or vane leading edge 160.

Additive manufacturing may be relied upon to make replacement components or replacement tips 170, which in combination with the brazing process and the particular brazing material enhance the operation of the repaired bucket or blade 155.

One preferred additive manufacturing process that is well suited for manufacturing the replacement component or replacement tip 170 includes atomic diffusion. Fig. 20-22 illustrate a process of repairing blade tips 165 using atomic diffusion to form replacement tips 170. As will be appreciated by one of ordinary skill, the same process may be applied to repair of the blade 155 or leading edge 160 of the bucket as well as other components not discussed herein.

Referring to fig. 20, atomic diffusion uses a binder and a metal powder to perform rapid structuring of a 3D shape. The metal powder is typically selected to closely match the material (e.g., alloy (CM) 247) used in the component being repaired (i.e., blade 155). The metal powder and the polymeric binder are mixed and then formed into the desired shape that will ultimately produce the replacement part or tip 170. This initial component 185 is commonly referred to as a "green form". The "green form" component 185 is then heated and sintered in a high temperature sintering operation to remove the binder and mechanically/metallurgically bond the powder particles. The sintering temperature is selected to allow complete removal of the binder while providing the desired mechanical/metallurgical bonding of the powdered metal without complete melting of the powdered metal particles.

One method of forming the green form component 185 includes 3-D printing techniques. Wire stock is prepared, comprising the desired powdered metal and binder. The user can incorporate material chemistry or custom chemistry as needed to achieve the desired material properties in the completed replacement tip 170 or replacement. In addition, different compositions may be used at different times during formation of the replacement tip 170 to achieve different characteristics at different locations within the replacement tip 170. For example, in one configuration, a composition intended to be the first layer or joining layer includes the desired base material and braze material incorporated into the wire stock.

To manufacture the replacement tip 170 or another component, a first layer or bonding layer is deposited onto the support structure 190 or formed separately from the support structure 190. The first surface in the example of fig. 20 is intended to be a surface that is joined or brazed to the component being repaired (i.e., blade 155) to attach the replacement tip 170 to the blade 155 being repaired. Additional layers may be formed on top of the first layer using the same material or another material that may be needed for a particular replacement component.

For example, the feedstock may be changed to a second material that does not include braze material and more closely matches the base material of the blade 155 or other component being repaired. As noted above, some materials may be employed that enhance the performance of the replacement tip 170 or other component to be superior to the performance of the base material. Any of these materials may also be used in the process. For example, up to 8% aluminum may be used to enhance oxidation resistance. As previously mentioned, the sintering process is designed not to melt the powdered material. Since the process is a non-melting process, no chemical change is expected to occur.

With continued reference to fig. 20, the metal powder is extruded with a binder (e.g., a polymer) to form a wire feedstock, which is then deposited onto the support structure 190. A ceramic intermediate layer 195 may be positioned between the deposited material and the support structure 190 to assist in removing the completed replacement tip 170 from the support structure 190. The cleaning step of the green structure removes the polymeric binder and densification is performed via sintering. Typically, since densification is achieved by solid state diffusion, densities greater than ninety-six percent may be achieved, but depending on the component size and corresponding wall thickness. An example of a replacement tip 170 formed using this process, after sintering, and removed from the support structure is illustrated in fig. 21.

The method does not experience isotropy of the layer-based AM technique and, due to the speed at which the method produces the green form part 185 and the very low powder waste, the method significantly reduces costs compared to other AM techniques. Additionally, as previously described, this additive manufacturing process may be used to form components other than replacement tips 170, including leading edge replacement or other components, and may include advanced features such as attachment structures 110.

Another advantage with this approach is that the component can be made of other high temperature resistant materials with better strength, oxidation resistance and coating adhesion, such as Oxide Dispersion Strengthening (ODS) or advanced single crystal (CMSX 8/Rene N5/PWA 1484).

In summary, fig. 20-22 illustrate replacement tips 170 during various states of fabrication using an atomic diffusion process. After the damaged portion of the tip 165 of the blade 155 being repaired is removed, the replacement tip 170 may be sized for manufacture. In many cases, the support structure 190 will be required to define the base of the support to which the replacement tip 170 may be formed. Although not required, in the case of the support structure 190, the ceramic intermediate layer 195 may be applied first to help easily separate the completed replacement tip 170 from the support structure 190.

The green form part 185 is then printed using raw materials of the appropriate composition. The first layer or layers may use raw materials as part of the base material, part of the adhesive, and part of the brazing material that is ultimately used during attachment of the replacement tip 170 to the blade 155. After printing out these initial layers, the raw materials can be converted into the following raw materials: the feedstock includes the desired base metal chemistry (i.e., the chemistry that closely matches the blade 155) and a binder, typically in the form of a polymer. The chemical composition of the subsequent feedstock may include enhanced chemical compositions as previously described to provide excellent material properties such as oxidation resistance.

After the 3-D printing process is completed, the green form part 185 is cleaned and sintered to remove the binder and mechanically or metallurgically bond the remaining particles into the desired shape. The sintered replacement tip 170 is removed from the support structure 190, as illustrated in fig. 21.

As illustrated in fig. 22, the replacement tip 170 is placed in place on the blade 155 and a braze joint 200 is formed between the replacement tip 170 and the blade 155. During the brazing process, the braze material in the initial layer or layers of the replacement tip 170 aids in the completion of the braze joint and attachment of the replacement tip 170.

Current materials for pre-sintered preforms (PSPs) and for braze materials are typically nickel (Ni) chromium (Cr) -based, with braze materials for use with nickel-based superalloy materials operating in high temperature environments (e.g., 1000°f, 538 ℃).

The compositions described herein are preferably applied to PSP and/or braze materials that do not include boron. To improve the creep rupture life of boron free PSPs and braze materials, rhenium (Re) or ruthenium (Ru) may be added to most nickel-based braze alloys. These two elements are powerful creep-resistant promoters added to the base metal component for improved creep rupture life. These two elements increase the creep resistance of the nickel-base alloy up to ten times. The high melting point and large atomic diameter of these two elements results in low atomic diffusivity and enables the nickel-based material to increase its creep resistance.

To date, rhenium (Re) and ruthenium (Ru) have not been added to boron-free brazing materials, as the need for creep-resistant brazing materials has been unknown.

For the addition of Re or Ru, the material is powdered and then mixed with the base material powder mixture prior to brazing. Re and Ru were added to the boron-free Ni-Cr-X braze/base material powder mix prior to PSP fabrication. Preferably, re and Ru have the smallest particle sizes possible for the powder. Preferably, the Re and Ru powder diameters are at least 50% or less than the base metal powder and the braze metal powder to ensure uniform mixing and homogeneous elemental distribution after brazing. Re and Ru powders do not melt during the brazing process. In contrast, re and Ru powders diffuse into the surrounding liquid braze material during brazing. These elements are transported uniformly in the brazing material due to the high diffusion rate in the liquid.

Re and Ru are added such that Re and Ru constitute 3 to 6 percent of the total composition of the braze or PSP, regardless of the ratio of base metal to braze powder in the braze.

For example, repair of a component made from alloy 247 may employ a PSP made from powder in which 74 to 77 percent match the alloy 247 composition, 20 percent match the desired brazing material (sometimes referred to as a melting point depressant), and 3 to 6 percent are one or both of Re or Ru.

Suitable braze materials are typically nickel-based and include nickel, chromium, and at least one of titanium, zirconium, and hafnium. Some specific braze components include components containing 6.5% Cr, 11% Zr, 7.5% Ti, and the remainder Ni. Another component may include 5.0% Cr, 10% Hf, 10% Zr, and the remainder Ni. Yet another component may include 17% Cr, 22% Ti, and the remainder Ni.

Each of the three components of the base material (74 to 77 percent), the brazing material (20 percent), and Re or Ru (3 to 6 percent) is powdered and mixed together for sintering. Re and Ru do not melt during any of the melting steps (i.e., the brazing process). Instead, re and Ru are dispersed through any melt pool during the melting process.

Fig. 3 illustrates one possible PSP insert 60 that may be manufactured using the materials described above. The PSP insert 60 is preformed and sintered to include the base material, braze material, and the desired amount of Re or Ru. FIG. 4 illustrates repair of a turbine bucket 30 using the PSP insert 60 illustrated in FIG. 3. After the damaged portion of the bucket 30 is removed, the required PSP insert 60 is sized and manufactured as described. The PSP insert 60 is then positioned in the empty space 55 in the bucket 30 and brazed in place. During the brazing process, some Re and Ru migrate into the liquid braze. Re and Ru do not melt in the pool, but will be embedded in the braze material during solidification.

Although exemplary embodiments of the present disclosure have been described in detail, those skilled in the art will understand that various modifications, substitutions, variations and improvements herein disclosed can be made without departing from the spirit and scope of the disclosure in its broadest form.

No description in the description of the present application should be read as implying that any particular element, step, act, or function is a basic element that must be included in the scope of the claims: the scope of patented subject matter is defined only by the allowed claims. Furthermore, unless the exact word "means for … …" is followed by a word, none of the claims are intended to refer to a means-plus-function claim structure.

Claims (15)

1. A method of forming a component, the method comprising:

mixing a powdered base material and a binder to define a mixture;

forming the mixture into a desired shape without melting the base material;

removing the adhesive from the desired shape to define a skeleton having a volume comprising between 80 and 95 percent of base material; and

infiltrating the skeleton with a melting point depressant material to define a finished pre-sintered preform having a porosity of less than one percent by volume,

wherein at least one of the mixture or the melting point depressant material comprises at least one of rhenium or ruthenium in powder form, and the total percentage of rhenium and ruthenium is 6% or less of the finished pre-sintered preform.

2. The method of claim 1, wherein the desired shape is heated to burn off the adhesive without melting the base material.

3. The method of claim 1, wherein the melting point depressant consists essentially of Ni, cr, and at least one of Ti, zr, and Hf.

4. The method of claim 1, wherein the melting point depressant consists essentially of 6.5% Cr, 11% Zr, 7.5% Ti, and the remainder Ni.

5. The method of claim 1, wherein the melting point depressant consists essentially of 5.0% Cr, 10% Hf, 10% Zr, and the remainder Ni.

6. The method of claim 1, wherein the melting point depressant consists essentially of 17% Cr, 22% Ti, and the remainder Ni.

7. The method of claim 1, wherein the finished pre-sintered preform is part of a leading edge of a turbine bucket.

8. The method of claim 1, wherein the melting point depressant contains an amount of Ti selected such that the pre-sintered preform has between 4% and 6% titanium.

9. The method of claim 1, wherein the desired shape is selected to replace a damaged portion of a turbine blade leading edge.

10. The method of claim 1, wherein the desired shape is selected to replace a damaged portion of a turbine blade tip.

11. A component, comprising:

a scaffold formed from a base material and defining a final shape of the component, the scaffold having a plurality of pores and a porosity of between 5 and 20 percent;

a melting point depressant material disposed within the skeleton, the melting point depressant material filling the pores within the skeleton to define a finished pre-sintered preform having a porosity of less than 1 percent by volume,

wherein at least one of the skeleton or the melting point depressant material comprises at least one of rhenium or ruthenium, and a total percentage of rhenium and ruthenium is 6% or less of the finished pre-sintered preform.

12. The component of claim 11, wherein the melting point depressant consists essentially of Ni, cr, and at least one of Ti, zr, and Hf.

13. The component of claim 11, wherein the melting point depressant consists essentially of 6.5% Cr, 11% Zr, 7.5% Ti, and the remainder Ni.

14. The component of claim 11, wherein the melting point depressant consists essentially of 5.0% Cr, 10% Hf, 10% Zr, and the remainder Ni.

15. The component of claim 11, wherein the melting point depressant consists essentially of 17% Cr, 22% Ti, and the remainder Ni.